[PATCH 1/2] xen/p2m: Fix for 32-bit builds the "Reserve 8MB of _brk space for P2M"

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

The git commit 5bc6f9888db5739abfa0cae279b4b442e4db8049
xen/p2m: Reserve 8MB of _brk space for P2M leafs when populating back.

extended the _brk space to fit 1048576 PFNs. The math is that each
P2M leaf can cover PAGE_SIZE/sizeof(unsigned long) PFNs. In 64-bit
that means 512 PFNs, on 32-bit that is 1024. If on 64-bit machines
we want to cover 4GB of PFNs, that means having enough for space
to fit 1048576 unsigned longs.

On 64-bit:
1048576 * sizeof(unsigned long) (8) bytes = 8MB

On 32-bit:
1048576 * sizeof(unsigned long) (4) bytes = 4MB

We fix that by using the above mentioned math instead of predefined
PMD_SIZE.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 arch/x86/xen/p2m.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index b2e91d4..626c979 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -198,7 +198,8 @@ RESERVE_BRK(p2m_mid_identity, PAGE_SIZE * 2 * 3);
  * max we have is seen is 395979, but that does not mean it can't be more.
  * But some machines can have 3GB I/O holes even. So lets reserve enough
  * for 4GB of I/O and E820 holes. */
-RESERVE_BRK(p2m_populated, PMD_SIZE * 4);
+RESERVE_BRK(p2m_populated, 1048576 * sizeof(unsigned long));
+
 static inline unsigned p2m_top_index(unsigned long pfn)
 {
 	BUG_ON(pfn >= MAX_P2M_PFN);
-- 
1.7.7.6